Method of making a cathode ray tube



July 1, 1967 MICHIO TAMURA METHOD OF MAKING A CATHODE RAY TUBE 2 Sheets-Sheet 1 Filed Nov. 6, 1963 by s y 11, 1957 V MICHIO TAMURA 3,330,682

METHOD OF MAKING A CATHODE RAY TUBE Filed Nbv. e. 1963 2 Sheets-Sheet 2 1111251172: I Ml'chio Emu ra United States Patent 3,330,682 METHOD OF MAKING A CATHODE RAY TUBE Michio Tarnura, Fujisawa, Japan, assignor to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Nov. 6, 1963, Ser. No. 321,820 7 Claims. (Cl. 117-33.5)

The present invention relates to the manufacture of screens for cathode ray tubes, and particularly to a method for manufacturing the screen of a color television tube.

A typical cathode ray tube for color television includes an electron gun, a multi-color fluorescent screencomposed of red, green and blue strip phosphors arranged in sequence on the inner face of the tube, and two or more groups of grids adjacent the fluorescent screen and extending in the direction in which the strip phosphors extend. This type of tube is known as the chromatron tube. This type of tube involves the application of a voltage on the grids called the post-deflection-focus-voltage. The variation of magnitude and polarity of the post-deflectionfocus-voltage produces converging electrostatic fields from the electron beams. These fields cause the beam electrons arriving at the grid wires from the electron gun to form a fine line structure on the phosphor target. As the potentials on the grid wires are changed selectively, the phosphor strips are caused to be energized selectively and thereby reproduces the color intelligence on the screen.

It has been found highly desirable to employ non-lumi-- nescing or opaque guard bands between the strips of phosphors to improve the, color, balance, brightness, resolution, and contrast of the television signals. These guard bands are particularly necessary in a three-phase chromatron tube although they can be used in two-phase systems as Well.

In order to position these guard bands properly at the precise predetermined locations necessary in the surface of the screen, an optical method and/ or an electron beam print method has been used. However, by the techniques of the prior art, it was found impossible to produce a guard band of significant mechanical strength and of sufficient thickness for the purpose. Furthermore, it was found that the guard band, which was usually a ceramic coloring agent consisting of a mixture of metallic oxides and carbon, could not be securely fixed to the inner surface of the cathode ray tube screen. Furthermore, the existence of the guard bands, which projected into the interior of the tube, made it difiicult to apply the phosphors.

It is accordingly an object of the present invention to provide a method for making a fluorescent screen for colored television tubes, said screen having improved guard bands located thereon.

Another object of the invention is to provide a method of making a fluorescent'screen having guard bands which are integral with the surface of the screen and do not project therefrom.

Still another object of the present invention is to provide a method for making a color television screen which is simpler than comparable methods previously used in the art.

A further object of the invention is to provide an improved color television tube having a screen including integrally formed guard bands.

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings in which:

FIGURES 1A to 1D illustrate schematically the steps involved in one suitable process for use in conjunction with the present invention;

FIGURES 2A and 2B illustrate a modified form of the invention;

FIGURES 3A to 30 illustrate a still further modified form;

FIGURES 4A and 4B illustrate the effect of the novel heating step upon the screen of the present invention;

FIGURES 5A to SF illustrate the steps involved in applying the phosphor strips upon the screen after the guard bands have been applied thereto.

One of the principal features of the present invention resides in the production of a non-luminous layer, specifically a guard band, by the thermal diffusion of metallic ions capable of reacting with the alkaline constituents of the glass into the glass to thereby cause the reaction and form an integral, opaque band in predetermined position along the face of the tube. The particularly preferred metals for use in this connection are silver and copper, in the form of their sulfides and/ or phosphates. Basically, the guard bands of the present invention are produced 'by applying the metallic salt to predetermined places on the cathode ray tube and then heating the glass face to a tem perature below its softening point, but sufficient to cause the reaction to occur between the metallic ions which migrate into the glass, and the alkaline constituents of the glass. Generally, temperatures on the order of 380 to 420 C. are satisfactory for most glasses, and treatment times of /2 hour to 1 hour are suflicient.

The staining which occurs when silver ions or the like migrate into the glass is believed due to the replacement of some alkali ions of the glass by an equivalent amount of silver. It is believed that this process actually involves four steps, the first being a base exchange reaction between the alkali metal ions and the metal ions, the second being the migration of the metal ions into the interior of the glass, the third being the reduction of the metal ions to neutral atoms, and the fourth being the formation of color centers by crystallization. Whatever the mechanism of reaction, it has been found that such migration of metallic atoms into the glass produces a completely satisfactory guard band which is flush with the surface of the glass and still possesses the proper opacity and non-luminescent characteristics.

A further description of the present invention will be made in conjunction with the drawings which illustrate various procedures involved, and the following specific examples.

Example I In the form of the invention illustrated in FIGURES 1A to ID, a layer 3 of an electron sensitive material such as Kodak Photo Resist (KPR) is uniformly applied onto .a transparent glass screen 2. In replacement of the specific material mentioned in the foregoing, other types of resins, such as polyvinyl alcohol can also be used, since these materials are sensitive to an electron beam such that they change their solubility characteristics in a solvent upon being exposed to the electron beam. Then a thin metallic layer 1 such as aluminum is coated on the surface of the electron sensitive layer 3. A potential of about 18 to 20 kilovolts is then applied to the conducting layer 1 and suitable potentials are applied to grids 11 and 12 to focus electron beams 4 at the predetermined positions on the face of the screen where the phosphor bands are to appear. After removal of the conducting layer 1, the thus coated and exposed panel is immersed in a developing solution, such astrichloroethylene to dissolve away the unexposed areas, leaving spaced strips 3' of the exposed resinous material. After this developing step, a slurry 5 composed of a photosensitive material and the silver or copper sulfide and/or phosphate is uniformly coated on the exposed areas 3' and then dried. A suitable composition of the slurry is given in the following table:

3 Ag S gr 1 Ag PO gr 2 KPR cc 6 KPR thinner cc 2 Following this application, the panel is then exposed to irradiation by ultraviolet light from behind the panel 2, as illustrated by reference numeral 15 in FIGURE 1C. This procedure results in the production of strips 5 containing the metallic salts, located between the areas 3".

Example ll As an alternative form of the invention, one may use the embodiment shown in FIGURES 2A and B, In this case, the slurry 5 containing the reactable metal salts is mixed directly with the electron sensitive material 3, thereby forming a layer 6 on the face of the glass 2. Then, upon the application of electron energy in the form of beams 4, and developing with a suitable developing solution, there are produced spaced strips 6' containing the electron sensitive material and the reactable salts. In this case, the areas 6 are located in precisely the arrangement desired in the guard bands of the finished tube.

Example III As another modification, the electron sensitive layer can contain electrically conductive particles such as graphite. A suitable composition for this purpose is given in the following table:

Graphite gr 80 KPR cc 2,000 KPR thinner cc 750 In this particular embodiment, the conducting layer 1 is not necessary since the electron sensitive layer containing the electrically conductive materials is itself sulficiently conductive.

Example IV In this modification, silver powder is mixed in the electron sensitive material 3, and a layer 7 is applied to the glass 2 as illustrated in FIGURE 3A. The layer 7 is then exposed to the electron beams 4, thereby producing, after developing, the exposed area 7' which include the electron sensitive material and silver powder. Then, a solution of hydrogen sulfide or hydrogen sulfide vapors are reacted with the areas 7' to obtain a layer 7 which contains silver sulfide in those areas in which the guard bands are to appear.

Example V To cause migration and reaction of the metallic ions into the surface of the glass, the coated glass having the areas 5, 6 or 7 containing the metallic salts are heated below the softening temperature of the glass, and usually on the order of 380 to 420 C. (preferably 400 C.) for about 30 to 60 minutes. Due to the dispersion of the metallic ions into the alkali metal constituents of the glass, opaque strips are formed, and reaction products appear at the surface of the glass plate 2. This material and any excess unreacted material can be washed away with a water rinse, leaving a brown colored layer 8 integral with the glass and flush therewith.

The colored layer 8 serves as a guard band which is non-luminescent and opaque. The layers do not project from the glass panel, and are of the same mechanical strength as the material in which they are located.

The following example illustrates the manner in which the phosphors are coated onto the inner face of the tube after the guard bands have been applied.

Exa'mple VI As illustrated in FIGURE 5A, a photosensitive material 9R containing, for example, a red phosphor is coated on the panel 2 and then exposed to a flood of ultraviolet light through an apertured mask 10. This irradiation causes photochemical hardening of the red phosphor material so that upon subsequent washing by means of a water solution or the like, a red phosphor strip layer 9R remains on the face of the tube as illustrated in FIGURE 5B. Next, a photosensitive material 9G is coated on the inner face of the tube, and over the previously applied red phosphor strip 9R. This material is then exposed to ultraviolet light through the mask 10 as shown-in FIG- URE 5C. Upon washing away the unexposed areas, only the green and red phosphor strip layers 9G and 9R remain, as illustrated in FIGURE 5D.

Similarly, as shown in FIGURE 5E, the blue phosphor layer is applied as a film 9B over the previously formed red and green phosphor strips, and over the inner face of the tube 2. Then, the tube is exposed to the action of ultraviolet light without the use of the mask 10 and, after washing away unexposed areas, there remain blue phosphor strips 9B in addition to the previously applied red and green phosphor strips 9R and 913 respectively, and shown in FIGURE 5F.

One of the advantages of the present invention resides in the fact that the irradiation with ultraviolet light need not be controlled to close tolerances as has been the practice heretofore. For example, the width of the aperture and the mask 10, illustrated at D in the drawings can be somewhat greater than the dimension d constituting the width of the finished strip since the previously applied guard strips 8 themselves serve as masks to confine the ultraviolet irradiation to the areas desired.

For the foregoing, it will be evident that the process of the present invention provides a simplified but highly effective means for applying guard bands onto the face of a cathode ray tube, and thereafter applying the phosphor strips in their correct orientation.

While the foregoing description has been made in connection with the chromatron type color cathode ray tube, it should be understood that the method of the present invention is also applicable to other types of cathode ray screens, such as those involving phosphor dots in a shadow mask type color cathode ray tube,

It should also be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. In the manufacture of a color screen for a glass cathode ray tube having a regular arrangement of color phosphors interspersed with a regular arrangement of guard areas, the improvement which comprises depositing a sensitized electron hardenable layer over the face of said tube, impinging electron beams in a predetermined pattern on the resulting layer, developing the exposed layer by treatment with a solvent for the unexposed areas to leave a regular arrangement of undissolved areas and bare areas therebetween, treating those of the areas in which the guard areas are to .appear with a salt of a metal capable of reacting with the alkali metal constituents of the glass to form a non-luminescent, opaque reaction product, heating the thus coated face to a temperature sufiicient for the aforementioned reaction to occur, and thereafter sequentially applying color phosphors in the others of said areas.

2. The method of claim 1 in which said metal salt is a silver salt.

3. The method of claim 1 in which said metal salt is a copper salt. I

4. The method of claim 1 in which said metal salt is silver sulfide.

5. The method of claim 1 in which the metal salt is silver phosphate.

6. The method of claim 1 in which said metal salt is copper sulfide.

7. The method of claim 1 in which said metal salt is cupric phosphate.

(References on following page) References Cited 2,858,233 10/1958 Yanagisawa et a1. 117-33.5

UNITED STATES PATENTS 2,873,189 2/1959 Evans et a1. 11733.5

11/1933 Rudenberg 117 335 2,916,0 2 1 9 9 Hergenrother 117 33 5 g; 13% 3 15-132 5 WILLIAM D. MARTIN, Primary Examiner. 4/1954 V;e:z :1 11733.5 ROTHSTEIN ATTAGUILE 8/1957 Crosby et a1. 117-33.5 Assistant Examl'lers- 

1. IN THE MANUFACTURE OF A COLOR SCREEN FOR A GLASS CATHODE RAY TUBE HAVING A REGULAR ARRANGEMENT OF COLOR PHOSPHORS INTERSPERSED WITH A REGULAR ARRANGEMENT OF GUARD AREAS, THE IMPROVEMENT WHICH COMPRISES DEPOSITING A SENSITIZED ELECTRON HARDENABLE LAYER OVER THE FACE OF SAID TUBE, IMPINGING ELECTRON BEAMS IN A PREDETERMINED PATTERN ON THE RESULTING LAYER, DEVELOPING THE EXPOSED LAYER BY TREATMENT WITH A SOLVENT FOR THE UNEXPOSED AREAS TO LEAVE A REGULAR ARRANGEMENT OF UNDISSOLVED AREAS AND BARE AREAS THEREBETWEEN, TREATING THOSE OF THE AREAS IN WHICH THE GUARD AREAS ARE TO APPEAR WITH A SALT OF A METAL CAPABLE OF REACTING WITH THE ALKALI METAL CONSTITUTENTS OF THE GLASS TO FORM A NON-LUMINESCENT, OPAQUE REACTION PRODUCT, HEAT- 